1. Technical Field
The present invention relates to lifting device, and more particularly to a lifting device that is designed to lift and lower an external object stably.
2. Description of Related Art
A table adjustable in terms of height is convenient and welcome by various users. There are thus lifting devices designed to lift and lower a table top to a desired altitude, such as Taiwan Patent No. M461623U1, titled “Lifting Device.” Referring to FIG. 1 and FIG. 2, the prior-art lifting device includes an upper seat 11, a gas struts 12 attached to the upper seat 11 from below, two supporting posts 13 extending downward from the upper seat 11, and a lower seat 14 for receiving the gas struts 12 and the supporting posts 13. The gas struts 12 has a piston rod 121 connected to the upper seat 11, and a cylinder tube 122 mounted around the piston rod 121. The supporting posts 13 are located at two opposite sides of the gas struts 12. Each of the supporting posts 13 has an outer peripheral surface 131, a plurality of rings 132 spaced and fitted around the outer peripheral surface 131, a plurality of balls 133 movably received in the rings 132, and a retaining block 134 fixed to the lower end of the outer peripheral surface 131 for preventing the rings 132 from escaping. The lower seat 14 has a vertical stand 141, a through hole 142 passing through the vertical stand 141 for receiving the cylinder tube 122 of the gas struts 12, and two sleeves 143 installed in the vertical stand 141 for receiving the two supporting posts 13. When the device is properly assembled, the balls 133 press on the outer peripheral surface 131 of the supporting post 13 and the inner peripheral surface 144 of the sleeve 143. Additionally, the upper seat 11 can be fixed to a table top 2 at the latter's bottom.
In use, by making the piston rod 121 expand and retract in the cylinder tube 122, the supporting posts 13 are driven to move upward or downward in the sleeves 143 as the balls 133 roll along the outer peripheral surfaces 131 of the supporting posts 13 and the inner peripheral surfaces 144 of the sleeve 143, in turn changing the altitude of the table top 2.
However, the function of the prior-art lifting device relies the rings 132 fitted around each of the outer peripheral surface 131 of the supporting post 13 and the balls 133 installed in the rings 132, which involve complicated and time-consuming assembling works. Besides, the contact between the balls 133 and both the outer peripheral surface 131 of the supporting post 13 and inner peripheral surface 144 of the sleeve 143 is point contact, which generates detrimental contact pressure at the contact points and tends to make the balls 133 become worn prematurely.